1. Field of the Invention
This invention relates to an ozonizer for producing ozone gas by supplying oxygen to a so-called xe2x80x9cdielectric barrier dischargexe2x80x9d which is caused on the two sides of a dielectric and, more particularly, to an improvement in a short-gap ozonizer having a discharge gap of 0.5 mm or less.
2. Description of the Related Art
In a device for generating ozone, as known in the prior art, the ozone gas is produced by supplying the oxygen gas to a so-called xe2x80x9cdielectric barrier dischargexe2x80x9d which is caused on two sides of the dielectric.
FIGS. 10 and 11 are a sectional view and a front elevation (of one half) showing the conventional ozonizer of the Otto plate type, as called and so disclosed on pp. 249 of xe2x80x9cOZONIZER HANDBOOKxe2x80x9d (edited by Ozonizer Expert Committee of Electric Society and published by CORONA in 1960). As shown, reference numeral 1 designates a discharging power source for generating a high voltage, and its one output is grounded. Numeral 2 designates an earthed electrode made of a metal; numeral 3 designates a high-voltage electrode disposed to face the earthed electrode 2 and connected with the high-voltage terminal of the power source 1; and numeral 4 designates a dielectric (as exemplified by a glass plate) placed on the surface of the earthed electrode 2 and on the surface of the high-voltage electrode 3. This dielectric 4 is covered with a metal on its side in contact with the earthed electrode 2 or the high-voltage electrode 3 for the power supply. The dielectric 4 is usually thin and is called a xe2x80x9cdielectric sheetxe2x80x9d.
Numeral 5 designates a discharging gap (as will be shortly called the xe2x80x9cgapxe2x80x9d) formed between the dielectric 4 on the earthed electrode 2 and the dielectric 4 on the high-voltage electrode 3, and numeral 6 designates a spacer for forming the discharging gap 5 to keep the two electrodes from contacting each other. Numeral 7 designates a supply port for supplying a gas including oxygen; numeral 8 designates an exhaust port for exhausting an ozonized gas; numeral 9 designates an exhaust pipe for the same; and numeral 20 designates a casing. In the example of FIGS. 10 and 11, the dielectric 4 is used on the two sides of the discharging gap 5. In the following individual Figures, the detailed description of identical or corresponding portions will be omitted by designating them by common reference numerals.
FIG. 12 and FIG. 13 show an ozonizer having a small gap (e.g., 0.5 mm or less), as disclosed in Unexamined Published Japanese Patent Application 8-12304, and FIG. 12 presents a sectional view whereas FIG. 13 presents a front elevation of a portion of the earthed electrode 2 and the dielectric 4. As shown, the numeral 2 designates a circular earthed electrode acting as an electrode and a container, and this earthed electrode 2 has a cooling passage 23 therein for allowing cooling water to pass therethrough. Arrows 211 designate the flows of the cooling water. The numeral 4 designates a disc-shaped dielectric made of ceramic, and this dielectric 4 has a conductive film 31 on its upper side for supplying the high voltage. Between the lower side of the dielectric 4 and the earthed electrode 2, there is disposed a radial spacer 61, by which a radial discharging gap 5 is formed between the dielectric 4 and the earthed electrode 2. Numeral 2200 designates a high-voltage terminal which is pushed onto the spacer 61 and the dielectric 4 through an interference spring 1002 thereby to form one discharge cell. In the example shown in FIG. 12 and FIG. 13, the dielectric 4 is disposed on only one side of the discharging gap 5, and the earthed electrode 2 has a water-cooled structure.
In the ozonizer of the prior art, an electrode conductive film is formed by a deposition or metallizing method or another method on one side of the dielectric 4 so as to bond the earthed electrode 2 and the dielectric 4, as well as the high-voltage electrode 3 and the dielectric 4. On the other hand, the size of the discharging gap 5 is far smaller (e.g., 1 mm or less) than that of the electrodes so that the spacer 6 or 61 having a predetermined thickness at the assembling time is sandwiched so as to hold that gap precisely. A high voltage is applied to establish a discharge between the two electrodes. When oxygen is supplied to the discharge, there occur the dissociation of oxygen and three-body collisions of oxygen atoms and oxygen molecules. As a result, ozone is produced.
It has been desired to enhance the ozone producing efficiency (i.e., the amount of ozone to be produced for a predetermined power) to be taken by the discharge. In the prior art, the efficiency is about 20% at the maximum. The ozone producing efficiency depends upon the discharging gas temperature (as seriously influenced by the electrode temperature) so that it is the higher at the lower temperature. However, most of the discharging power is converted into heat at the earthed electrode 2 and the high-voltage electrode 3 so that the temperatures of the electrodes rise. In order to enhance the ozone producing efficiency, therefore, the electrodes 2 and 3 are forcibly cooled with water or the like.
On the other hand, FIG. 14 presents a graph, as disclosed in FIG. 4 of the aforementioned Unexamined Published Japanese Patent Application 8-12304. In this graph, relations between the size t of the discharging gap 5 and the ozone producing efficiency xcex7 are illustrated by using a gas pressure as a parameter. As seen from FIG. 14, the efficiency can be improved for a smaller gap if the gas pressure is accordingly raised. Therefore, it has been desired to make the gap as small as possible.
In order to enhance the ozone producing efficiency, as described above, the ozonizer of the prior art has to make the discharging gap smaller. In order to keep the electrodes at a low temperature, on the other hand, it is also necessary to provide the cooling passage 23 for the cooling water in the electrode. If this electrode is thus cavitated, its surface is slightly deformed by the water pressure. The degree of deformation fluctuates due to fluctuation in the water pressure. This deformation or its degree raises no serious problem when the gap is large. For the smaller gap, their influences becomes the more serious. It is, therefore, very difficult to make the gap as small as about 0.1 mm.
In the ozonizer of the prior art, as described above, the dielectric sheet 4 having a thickness of about 1 mm is bonded to the electrode, and the spacer 7 or 61 for forming the discharging gap 5 is integrated with the dielectric sheet 4 by flame-spraying a ceramic to a portion of the electrode or the dielectric sheet 4. Therefore, the adjustment of the gap is seriously difficult because the flame-spraying treatment has to be done again or because the flame-spraying surface has to be scraped.
If the individual discharging gaps are of a size when they are formed in multiple stages by laminating the electrodes, on the other hand, the gas containing oxygen can be supplied at a pressure suited for the gaps so that the overall efficiency is improved. With a dispersion in the gaps, however, the optimum pressure is also dispersed to lower the overall efficiency.
On the other hand, the dielectric sheet 4 is merely sandwiched or adhered between the spacer and the electrode. With a high flatness or warpage of the dielectric sheet 4, therefore, there occurs a problem that the ozone producing efficiency is lowered by an insufficient contact between the dielectric sheet 4 and the electrode or that the dielectric sheet 4 itself cracks in the bonding work.
With the problems thus far described, it is resultantly difficult to enhance the ozone producing efficiency. Since the conventional dielectric sheet is made thin, on the other hand, it takes a polishing work lengthy to manufacture a dielectric sheet which is so accurate as to have a planarity with little warpage. This long polishing work leads to a problem in raising the cost significantly.
The invention has an object to provide an ozonizer achieving a narrower gap easily and adjusting a gap (i.e., a distance between a pair of flat electrodes) easily.
Another object is to provide an electrode structure which is hardly deformed by changes in water pressure and temperature.
Still another object is to provide a hardly deformed dielectric sheet at a low cost.
Thus according to the invention, there is provided an ozonizer comprising: a pair of flat electrodes arranged to face each other and having a hole portion formed in the facing side of at least one of the paired flat electrodes; a dielectric sheet disposed on the facing side of at least one of the paired flat electrodes; high-voltage applying unit for applying a high voltage between the paired flat electrodes; gas supply unit for supplying a gas containing oxygen to a gap formed between the paired flat electrodes; a spacer so fitted in the hole portion as to protrude from the surface of the flat electrode having the hole portion, for forming the gap with the protrusion; and an adjusting member such as an adjusting sheet and an adjustiong screw and so on for adjusting the height of protrusion of the spacer.
In this invention, the spacer inserted in the hole portion is thicker than the gap so that it can be easily handled, and the spacer is fitted in the hole portion so that it does not come out at the assembling time. By the adjusting member, the height of the protrusion of the spacer can be easily adjusted to adjust the size of the gap which is determined by the protrusion of the spacer.
On the other hand, at least one flat electrode includes a cooling passage for allowing a coolant to pass therethrough, and a reinforcing member extending from the front face to the back face of the flat electrode through the cooling passage. Then, the surface of the flat electrode can be prevented from being deformed by the pressure of water flowing in the cooling passage.
On the other hand, the flat electrode having the dielectric sheet arranged thereon has a recess in its facing side, and the dielectric sheet has such a projection on its side of the flat electrode as is fitted in the recess. The dielectric sheet can be firmly held on the flat electrode and prevented from warping or cracking. Moreover, the dielectric sheet is wholly made of one sintered body together with the projection. As a result, the thermal distortion of the dielectric sheet due to the high temperature at the sintering time can be absorbed by the projections to provide a sheet having a high parallelism and little warpage. Moreover, the time period for shaping the dielectric sheet by the polishing treatment can be drastically shortened to result in a low cost.